docs: fix Ruby Lua function signature

Signed-off-by: Loi Nguyen <vanloi999@gmail.com>

Author: lntutor

src/content/docs/how-to/load-and-execute-functions.mdx

@@ -417,9 +417,9 @@ The following example shows a simple example of loading and executing a Valkey F
          ```ruby
          lua_code = <<~LUA
            #!lua name=example_module
-           server.register_function('set_then_get', function(key, value)
-              server.call('SET', key, value)
-              return server.call('GET', key)
+           server.register_function('set_then_get', function(keys, args)
+              server.call('SET', keys[1], args[1])
+              return server.call('GET', keys[1])
            end)
          LUA
          ```